This invention relates to interior trim articles containing a panel structure mountable in a vehicle to form a part of the interior thereof, and in particular to automobile interior trim articles, such as instrument panels and door panels, which conceal a secondary restraint system including an air bag. This invention further relates to a process for making the aforementioned interior trim articles.
The escalation of the commercial significance of air bag restraint systems in automobiles as secondary restraint systems has manifested itself in the appearance of air bag restraint systems in many, if not most, new automobiles. The commercial impact of such secondary systems is attributable both to government regulations and consumer demand for safety.
Generally, air bag restraint systems are concealed from view during normal operation of the vehicle by arranging the air bag restraint systems behind automotive interior trim articles, such as instrument panels and/or door panels.
In order to permit the deployment of the air bags upon collision of the vehicle, interior trim articles are often formed with a multi-layered structure comprising a rigid substrate having hidden doors formed therein, an outer decorative skin layer, and a soft cellular polyurethane foam layer formed therebetween. The hidden doors of the rigid substrate are configured and arranged in such a manner that the edges of the doors define discernible patterns, such as patterns in the form of H, C, U, and X shapes.
During deployment of the air bag, the air bag is actuated via a gas generating system and expands from a folded, undeployed state to an inflated, deployed state. The expansion of the gas inflates the air bag against the backside of the hidden doors and forces the hidden doors to open into the passengers"" compartment of the vehicle. The emergence of the hidden doors into the passengers"" compartment creates a passageway which permits deployment of the air bag into the passengers"" compartment of the vehicle. The deployed air bag protects the driver and passenger from violent collision against the panel structure.
In order to minimize obstruction of the passageway through which the expanding air bag traverses, the underside of the outer skin can be provided with structurally weakened tear seams. These tear seams often take the form of perforated or channel-like patterns, and are constructed and arranged to substantially correspond to and overlay the pattern (e.g., H-shaped) defined by the edges of the hidden doors of the substrate. During deployment of the air bag, the outer skin tears or fractures along the structurally weakened tear seams. Absent the presence of such structurally weakened tear seams in the outer skin, the outer skin may possess sufficient internal strength to resist fracture upon deployment of the rapidly expanding air bag. If the skin does not fracture, the entire outer skin can become separated from the rigid substrate and/or the multi-layered structure can be dismounted from the vehicle frame, thereby imperiling the safety of the driver and passengers.
Different techniques have been proposed to form a multi-layered structure having an outer skin with a structurally weakened, rupturable tear seam. One conventional technique involves the preparation of a rotational-cast poly(vinyl chloride) (xe2x80x9cPVCxe2x80x9d) skin by providing a powder box including a seam-defining structure or gasket, which partitions the powder box into two chambers. A PVC powder with appropriate colorants and additives, such as plasticizers, is retained in each of the chambers. Where a dual-tone appearance is desired, the chambers can be supplied with PVC powders containing different colorants, in which case the seam-defining structure simultaneously serves as a color division rim. The powder box is then engaged to a metal mold component to define a closed casting system having the seam-defining structure closely spaced from a heated mold surface of the metal mold component. The PVC powder is then tumbled against a heated molding surface of the metal mold by a rotational casting method until the PVC powder is formed against a moderately heated mold surface in a gelled state. Excess powder collects in the powder box, and is thereafter separated and removed from the mold. Since the seam-defining structure obstructs the gelling of PVC powder on the portion of the heated mold surface therebelow, the structurally weakened portion of the skin is formed below the seam-defining structure. A lower density or lower strength tear seam material (also referred to as a filler material) is then sprayed into the perforated or channel-like seams and gelled. The gelled PVC material and the gelled tear seam material are then fused by heating the materials to their fusion temperatures, and thereafter cooled to provide the PVC-based covering in a thermoplastic solid state. The skin can then be united with the rigid substrate, such that the low density material of the outer skin is positioned to substantially correspond to and overlay the edges of the hidden doors.
There are at least two problems associated with the above-described conventional method. First, the presence of the seam-defining structure hinders the normal compacting of the PVC powder which occurs during rotation of the closed system. Hence, the portion of the skin layer corresponding to the structurally weakened tear seam possesses a greater porosity than the remainder of the skin. The difference in porosity between the structurally weakened portion and the remaining portion of the outer skin makes the pattern of the tear seam visible, especially in bright light. The second problem is due to the difference in composition of the cast skin and the sprayed tear seam material. In top-mount applications in which the tear seam is exposed to high temperatures and intense UV radiation, the sprayed material introduced into the tear seam ages differently than the surrounding cast material and will become clearly visible over time. For these reasons, multi-layered structures made by the aforementioned conventional method are only effectively employed in mid mount applications where the hidden tear seam is not exposed to direct sunlight.
In order to overcome these problems, it has been proposed to form a PVC skin layer of uniform thickness, and thereafter form the structurally-weakened tear seams by laser cutting the backside of the skin. Due to the relatively small thickness of the skin, however, it is very difficult to precisely control the depth of the cut portion. Consequently, errors in laser cutting can lead to the disposal of skins as unusable scrap. In addition, the capital investment associated with obtaining and operating a laser cutting apparatus is very high.
A need therefore exists to provide a process for making a panel structure containing a decorative covering having an inner surface with a structurally weakened tear seam in which the tear seam is concealed from view, even after employing the covering in top mount applications which subject the covering to prolonged use and exposure to high temperatures and intense UV radiation.
The disadvantages of the prior art may be overcome by providing a process for making a panel structure comprising a layered composite structure and a reinforcing substrate including a door structure movable through a portion of the layered composite structure upon the operation of the secondary restraint system. The panel structure is mountable to a vehicle to form a part of the interior thereof in concealing relation to a secondary restraint system.
In accordance with one embodiment of this inventive process, the layered composite structure is formed on a mold surface, the layered composite structure comprising an outer layer with an exterior surface having an opaque visual appearance, a seam defining structure configured to define an exteriorly invisible tear seam generally corresponding with portions of an outline of the door structure movable through the layered composite structure during the operation of the secondary restraint system, and an inner layer having a frangible line along the exteriorly invisible tear seam by virtue of the presence of the seam defining structure. The layered composite structure is united with the reinforcing substrate so that the reinforcing substrate reinforces the layered composite structure in such a way that the narrow elongated structure and the reduced thickness portion of the inner layer along the invisible tear seam causes the layered composite structure to fracture generally along the invisible tear seam in response to the movement of the door structure through the layered composite structure during the operation of the secondary restraint system. Optionally, a soft cellular foam layer can be interposed between the layered composite structure and the reinforcing substrate.
In accordance with another embodiment of this inventive process, the layered composite structure is formed on a mold surface and comprises an outer layer with an exterior surface having an opaque visual appearance and an inner layer adhered to the outer layer and including a seam defining structure in the form of a severed sheet structure through which the door structure moves during the operation of the secondary restraint system. The layered composite structure and the substrate are united so that the substrate reinforces the layered composite structure. The sheet structure is severed to define an exteriorly invisible tear seam generally corresponding with portions of an outline of the door structure. The severed portion defining the invisible tear seam causes the layered composite structure to fracture generally along the invisible tear seam in response to the movement of the door structure through the layered composite structure during the operation of the secondary restraint system. A soft cellular foam layer optionally can be interposed between the layered composite structure and the reinforcing substrate.
Other objects of the invention are achieved by providing an article comprising a panel structure made by the above-mentioned embodiments of the inventive process of this invention.
Since the layered composite structures provided in accordance with the above-discussed embodiments have an outer layer that can be uniformly sprayed onto heated mold surface without requiring a seam-defining structure for forming a structurally weakened seam in the outer layer, the outer layer of the composite structure does not exhibit the non-uniform porosity that characterizes conventional skins. Further, the outer layer assists in masking and concealing the non-uniform porosity and/or differentials in aging between the portion of the layered composite structure defining the structurally weakened tear seam.
The layered composite structure of this invention also exhibits excellent chemical, scuff and mar resistance to external influences. Further, appropriate additives can be introduced into one or more of the layers of the layered composite structure to provide the composite structure with the non-reflective and low gloss surface appearance desired for such panel-like structures.
Furthermore, both the inner and outer layers of the layered composite structure are characterized by excellent extensibility, such that the layered composite structure can withstand indentation and flexure during use without resulting in cracking in the outer layer over a wide temperature range, such as from xe2x88x9230xc2x0 C. to 120xc2x0 C.
The principles of this invention enunciated above are applicable to all types of skinned panel structures through which an air bag might deploy, but have particular applicability to instrument panels (also referred to as dashboards), door panels, steering wheels, pillar covers, headliners, and rear interior quarter panels. Moreover, the principles of this invention are applicable to various types of automotive vehicles, including passenger cars, trucks, vans, utility vehicles, and others.